Managing the level of pH is a critical component of maintaining water chemistry, particularly in aquatic applications such as swimming pools, water parks, spas and the like. Among the reasons is that pH determines the effectiveness of the chlorine used to treat the water. The type of chlorine also impacts both pH and total alkalinity because different types of chlorine have very different pH levels. Low pH can cause damage to pool liners and etching of plaster, corrosion of metal components in and around the pool, and skin and eye damage. On the other hand, high pH water can cause scale formation, metal stains, cloudy water, poor efficiency of chlorine, and also can cause skin and eye irritation.
Unlike pH—which is basically a scale to measure against—total alkalinity is a measurement of all alkaline substances dissolved in the water. These substances are primarily hydroxides, carbonates and bicarbonates, along with a few others. These alkaline substances buffer pH in the water. In other words, total alkalinity is a measurement of the water's ability to resist change in pH. Having the right level of total alkalinity aids in keeping the pH level stabilized.
The total alkalinity of a body of water is normally measured through a titration process. Starting with a known volume of the water to be tested, a strong acid is added (typically one calibrated a drop at a time), mixing as necessary, until the pH falls to a specified value. Using the known initial volume of water and the known volume of added acid, one can compute the total alkalinity using conventional calculations.
This conventional method works well for a still body of water. However, in certain applications, including most aquatic applications, specifically a recirculating water system, the total alkalinity for a flowing stream of water is required.
When the water is recirculated, as in aquatic applications, special care must be taken in performing the alkalinity measurement. Adding a strong acid to a recirculating system for the purpose of measuring alkalinity can adversely affect the pH of the entire body of water, especially in small bodies of water such as spas and slash pads.